Electrowetting-induced fluid propulsion enables pump-free tunable stiffness for soft actuator

Abstract

Compared with traditional rigid actuators, soft actuators offer enhanced safety and adaptability with the environment, whereas hydraulic-based soft actuators still face a major challenge: the need for additional external driving components such as pumps and valves leads to increased bulkiness, additional weight, and low system integration. Here, a novel method utilizing electrowetting-induced fluid propulsion is proposed to achieve pump-free reversible rapid actuation and tunable stiffness for soft actuator. By establishing the relationship among the electrowetting voltage, Laplace pressure difference, and the deformation/stiffness of the actuator, this work elucidates the mechanism of electrowetting-induced actuation and tunable stiffness (EIAS). Theoretical formulas are derived to verify the validity and feasibility of the EIAS, enabling effective prediction of its performance. Both the deformation performance and stiffness modulation of EIAS model increase with voltage while decrease with chamber wall thickness. Additionally, the optimum configuration of the EIAS model was obtained by considering the influences of the chamber material, configuration, height, length, and spacing on deformation and stiffness modulation performance. The optimal model demonstrates a maximum stiffness variation ratio of 2.72, bending angle of 52°, and relative deformation of 0.2704. These findings will open the door to achieving pump-free reversible rapid deformation and tunable stiffness for soft actuators, and will provide tremendous inspiration for the design of the hydraulic-based soft actuators.